extern "C" is used in C++ to declare a function or variable that has been defined in another file or library. It informs the compiler that the function or variable is defined externally and not in the current file. This is often used when working with libraries or when you need to use functions that are defined in another file.
When you use the `extern "C"` syntax
it tells the compiler to use C language linkage for the function or variable. This is important because C++ uses name mangling to handle function overloading and default arguments
but C does not. By using `extern "C"`
you ensure that the function or variable is accessed using C linkage
which means that the name will not be mangled and can be easily linked to the external definition.
For example
suppose you have a function called `foo` that is defined in a separate library. You can declare this function in your C++ code using the `extern "C"` syntax like this:
```cpp
extern "C" void foo();
```
This tells the compiler that the function `foo` is defined externally using C linkage. When the program is linked
the linker will be able to find the definition of `foo` in the external library and properly link it to your code.
Using `extern "C"` can be especially useful when working with C libraries in a C++ project. Since C and C++ have different name mangling schemes
using `extern "C"` ensures that the C++ code can properly interface with the C library.
In summary
`extern "C"` is a useful tool in C++ when working with external functions or variables that are defined in C or in separate libraries. It ensures proper linkage and allows for seamless integration between C and C++ code.
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